Article IV, Section 4 requires "The United States shall...protect each of them against Invasion," making federal defense of states from foreign threats a constitutional obligation. The Guarantee Clause, as Section 4 is known, also promises states a republican government and, upon request by state legislatures or governors, protection against domestic violence.
James Wilson introduced this language at the Constitutional Convention, and delegates approved it unanimously. The federal invasion protection clause assigns national defense exclusively to Washington, preventing states from maintaining armies or conducting foreign policy independently.
The Supreme Court ruled in 1849 that Guarantee Clause questions are "political, and not judicial," meaning courts generally won't intervene in disputes over whether the federal government fulfilled its protection duties. This leaves enforcement to Congress and the President. Recent border debates have revived the clause, with Texas officials claiming migrant crossings constitute an invasion, though most legal scholars reject that interpretation as inconsistent with the Framers' intent.
The Constitution obligates the federal government to defend states from foreign attack. This makes national defense a federal responsibility, preventing states from negotiating separately with foreign powers or maintaining their own armies.
People sometimes refer to migrant crossings as "invasions" and cite this clause as allowing state military action. "Invasion" in the Constitution means foreign military attack, not immigration. Immigration enforcement is federal authority.
The Constitution obligates the federal government to defend states from foreign attack. This makes national defense a federal responsibility, preventing states from negotiating separately with foreign powers or maintaining their own armies.
People sometimes refer to migrant crossings as "invasions" and cite this clause as allowing state military action. "Invasion" in the Constitution means foreign military attack, not immigration. Immigration enforcement is federal authority.